The present invention is generally related to lock assemblies for sliding closure members and, more particularly, to drop lock assemblies for sliding glass windows and doors. Although the invention is applicable to sliding closure members in general, including both doors and windows, the invention will be described below primarily with reference to conventional sliding windows of extruded aluminum frame construction.
Sliding windows are sometimes provided with a device known as a drop lock, which is slidably mounted on one edge of a movable window frame and which includes a downwardly projecting lock bolt that is insertable in one or more holes in the window sill. To lock the sliding window, the drop lock is typically mounted on a vertical side of the frame and slid downwardly to engage the lock bolt in a hole so as to prevent sliding movement of the window.
Previously available drop locks for sliding windows have proven unsatisfactory for various reasons. Some such locks cannot be retrofitted onto preexisting window frames without modification of the frames. Other drop locks have no provision for being secured in their locked position, with the result that they are subject to tampering and picking with any suitable device, for example, a stiff wire, that may be used to engage the drop lock and lift it upwardly from its locked position. Some drop locks include locking devices, for example, set screws, but such devices must typically be actuated separately and independently from the sliding motion of the drop lock, such that the drop lock is frequently left inadvertently in a locked but unlatched position.
Accordingly, it is the object of the present invention to provide an improved drop lock for a sliding closure member, particularly a sliding window or door.
More particularly, it is an object of the present invention to provide a latching drop lock for a sliding window or door. In this regard, it is another object of the invention to provide a latching drop lock that is easy to unlock and yet which is secure against tampering or picking while locked.
It is another object of the present invention to provide a locking drop lock that can be retrofitted onto preexisting extruded aluminum window frames. More particularly, it is an object to provide such a lock that may be retrofitted onto sliding window frames of the type ordinarily mounted on rollers for sliding motion.
It is yet another object of the invention to provide a drop lock that is automatically latched against unlocking movement each time it is lowered to its locked position.